Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $54.54   10.832%   $60.4478   $60.45   $60.45   $60.40  
  Purchase #2 $189.33   6.498%   $201.6327   $201.63   $201.65   $201.60  
  Purchase #3 $222.93   10.710%   $246.8058   $246.81   $246.80   $246.80  
  Purchase #4 $233.94   11.585%   $261.0419   $261.04   $261.05   $261.00  
  Purchase #5 $53.44   10.350%   $58.971   $58.97   $58.95   $59.00  
  Purchase #6 $44.59   13.503%   $50.611   $50.61   $50.60   $50.60  
  Purchase #7 $127.72   13.413%   $144.8511   $144.85   $144.85   $144.90  
  7 purchase totals = $926.49       $1,024.3613   $1,024.36   $1,024.35   $1,024.30